Control for refrigeration system centrifugal compressor

ABSTRACT

A REFRIGERATION SYSTEM IS PROVIDED WITH A CENTRIFUGAL REFRIGERANT GAS COMPRSSOR HAVING MOVABLE CAPACITY CONTROL MEANS IN ITS INLET AND A FLUID PRESSURE RESPONSIVE PISTON IS MOVABLE TO MOVE THE CAPACITY CONTROL MEANS ACCORDINGLY. FIRST AND SECOND SOLENOID OPERATED FLUID VALVES ARE ARRANGED TO BE NORMALLY DEENERGIZED IN A SYSTEM TO SUPPLY FLUID PRESSURE EQUALLY TO BOTH SIDES OF THE PISTION AND MAINTAIN THE CAPACITY CONTROL IMMOVABLE AT A PARTICULAR CAPACITY POSITION. WHEN A RESPECIVE ONE OF THE VALVES IS ENERGIZED, THE PISTION WILL BE MOVED IN A RESPECTIVE DIRECTION TO CHANGE THE POSITION OF THE CAPACITY CONTROL AND INCREASE OR LOWER THE CAPACITY CONTROL, ACCORDINGLY. A REFRIGERATION SYSTEM CONDITION SENSING CONTROL RESPONDS TO PROVIDE A RESPECTIVE ELECTRIC ENERGIZING SIGNAL TO THE RESPECTIVE VALVE SOLENOID IN THE FORM OF AN INTERMITTENT SIGNAL INCREASING IN FREQUENCY AND/OR DUTY CYCLY TO A CONTINUOUS SIGNAL AS THE SENSED CONDITION LOWERS OR RISES FROM A PRESET CONDITION, RESPECTIVELY, THUS INCREASING CAPACITY CONTROL SENSITIVITY WITHOUT INSTABILITY ABOUT THE PRESET CONDITION.

Oct. 5, 1971 0. K. RICHARDSON CONTROL FOR REFRIGERATION SYSTEM CENTRIFUGAL COMPRESSOR Filed April 15, 1970 2 Sheets-Sheet l EVAPORATOR CHILLER FIG. I

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Oct. 5, 1971 RlCHARDSON 3,609,989

CONTROL FOR REFRIGERATION SYSTEM CENTRIFUGAL COMPRESSOR Filed April 15, 1970 2 Sheets-Sheet 2 FIG. 2 5| VA VB PEN CLOSE WITNESSES INVENTOR Douglas K. Richardson ATTORNEY United States Patent CONTROL FOR REFRIGERATION SYSTEMv CENTRIFUGAL COMPRESSOR Douglas K. Richardson, Stannton, Va., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa.

Filed Apr. 15, 1970, Ser. No. 28,678 Int. Cl. F25b 41/04 US. Cl. 62202 9 Claims ABSTRACT OF THE DISCLOSURE A refrigeration system is provided with a centrifugal refrigerant gas compressor having movable capacity control means in its inlet and a fluid pressure responsive piston is movable to move the capacity control means accordingly. First and second solenoid operated fluid valves are arranged to be normally deenergized in a system to supply fluid pressure equally to both sides of the piston and maintain the capacity control immovable at a particular capacity position. When a respective one of the valves is energized, the piston will be moved in a respective direction to change the position of the capacity control and increase or lower the capacity control, accordingly. A refrigeration system condition sensing control responds to provide a respective electric energizing signal to the respective valve solenoid in the form of an intermittent signal increasing in frequency and/ or duty cycle to a continuous signal as the sensed condition lowers or rises from a preset condition, respectively, thus increasing capacity control sensitivity without instability about the preset condition.

CROSS REFERENCES TO RELATED APPLICATIONS A centrifugal gas compressor capacity control to which the control system of the invention may be applied is described and claimed in the copending patent application of Douglas K. Richardson and John G. Johnson, Ser. No. 14,471, filed Feb. 26, 1970. It should be understood however that the capacity control condition sensing system of this invention may be applied to any form of centrifugal compressor having any form of movable capacity control in its inlet in arrangements that may be different from that described in the above-mentioned copending application.

BACKGROUND OF THE INVENTION US. Pat. 3,350,897 to Plaster issued Nov. 7, 1967, described a capacity control system for a centrifugal gas compressor as used in a refrigeration system and the arrangement is such that there is a dead band of response to the sensed refrigeration condition about the desired preset condition. It may be desirable to minimize or eliminate the dead band type of sensing response for the capacity control when increased sensitivity and accuracy of control is desired but then problems of control instability about the preset condition may be encountered.

SUMMARY OF THE INVENTION In accordance with this invention, the first and second electrically energized valves for changing the capacity control of the centrifugal refrigerant gas compressor to maintain a desired preset condition of the refrigeration system are controlled to be energized by respective electrical control signals from a refrigeration system condition sensing control means that responds to very small deviations of sensed condition from the preset condition to thereby minimize the dead band of response. In order to preserve the stability of the system response about the preset condition, the control means of the invention genice crates an electrical control signal to the respective valve solenoid that is at first intermittent as the sensed condition begins to deviate from the preset condition and increases in frequency and/or duty cycle to a continuous electric signal as the sensed condition may deviate further from the preset condition. Thus small incremental changes in the position of the compressor capacity control are made within a given period of time for slight deviations of sensed condition and the stability of response of the system is assured even with much greater sensitivity of response to the preset condition.

Further features and advantages of the invention will be apparent with reference to the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic view of the refrigeration system embodying this invention;

FIG. 2 is a diagrammatic and fragmentary sectional view of the mechanism for adjustment of the capacity control of the centrifugal compressor;

FIG. 3 is an enlarged sectional view of the two interconnected solenoid adjusted valves of FIG. 2, the pistons of the valves being shown in the positions they take when the solenoid coils of the two valves are deenergized;

FIG. 4 is a view similar to FIG. 3 except that one solenoid coil, the left one, is energized;

FIG. 5 is a view similar to FIG. 4 except that the other solenoid coil, the right one, is energized;

FIG. 6 is a fragmentary perspective view of one form of condition sensing control switch of the invention; and

FIG. 7 is a wiring diagram for portions of the electrical control circuit as may be used in the system of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 of the drawings discloses a refrigeration system having an electric motor 10 connected to drive the refrigerant gas centrifugal gas compressor 11 whose compressed gas output passes through conduit 12 to the condenser 13. Liquid refrigerant in line 14 is expanded through the expansion device 15 and passes through the conduit 16 to the evaporator chiller 17. The suction line 18 connects the expanded refrigerant gas at low pressure back to the intake 19 of the centrifugal compressor 11. The centrifugal compressor 11 may be of any suitable type and is provided with capacity control means in its inlet 19 which may be of any suitable form such as the type shown in the aforementioned copending patent application or the spin vane type briefly shown by FIG. 2 of the drawings. The electric motor 10 may be powered through a pair of conductors 20 and 21 and a current sensing coil 22 is placed about the conductor 21 to provide a voltage signal for operating the overload relay OR when the current draw of the electric motor 10 exceeds a predetermined amount indicative of overloading of the motor or compressor. The evaporator chiller 17 is shown to be of the type having a system water inlet 25 and a cooled or chilled water outlet 26. Although the capacity control of the invention being described may respond to any desired sensed condition of the refrigeration system such as refrigerant pressure, refrigerant temperature or the like, the preferred arrangement being described in connection with FIG. 1 employs a temperature sensing element 27 adjacent the chilled water outlet 26 of the evaporator 17. The temperature sensing element 27 is connected to the condition sensor 30 for operating the condition sensor contacts Ca or Cb respectively as the sensed temperature condition of the chilled Water 26 may vary about a desired preset condition.

Referring to FIG. 2 of the drawings, a fluid pressure system for actuating or operating the centrifugal compressor capacity control will be briefly described, although if a more detailed understanding of such a system is desired reference may be made to the aforementioned Pat. 3,350,897. The inlet cone 40 of the centrifugal compressor is provided with a plurality of movable spin vanes such as the one shown at 41 and it should be understood that the rotatable position of the spin vane 41 as it may be rotated about its axis 42 will vary the capacity of the centrifugal compressor in a manner well known to those skilled in the art. A piston 43 is slidable within a cylinder having cylinder portions 44 and 45. When fluid under pressure is supplied to cylinder portion 44 and drained from cylinder portion 45 the piston 43 will move to the right in a manner to rotate the capacity control means or vane 41 to a position opening the intake and increasing the capacity of the compressor. But, if on the other hand, fluid under pressure is supplied to cylinder portion 45 and drained from cylinder portion 44 the piston 43 will move to the left of the drawings and its mechanical coupling to the capacity control at vane 41 will be such as to rotate the vane to a position corresponding to a closing of the centrifugal compressor intake and reducing the compressor capacity. When fluid under pressure is suppled equally to both cylinder portions 44 and 45, the capacity control piston 43 will remain in a given position corresponding to a given capacity of the compressor. Solenoid operated valves VA and VB are double acting valves as shown more in detail by FIGS. 3-5 of the drawings for supplying fluid under pressure selectively to either or both of the cylinder areas 44 and 45 and for selectively draining fluid under pressure from either cylinder areas 44 or 45.

As shown by FIG. 3 of the drawings, both solenoid valves VA and VB are shown in their deenergized position with their solenoid coils SA and SB not connected to a source of electric energizing potential. When the valves VA and VB are in the deenergized position as shown by FIG. 3 of the drawings, fluid under pressure in the line 52 is passed through needle valves 53 and 54 and through conduits 50 and 51 to both respective cylinder portions 44 and 45 thus balancing the capacity control piston 43 at a preset position.

As shown by FIG. 4 of the drawings, if the solenoid SA is energized the valve VA will be operated to allow the pressure of the cylinder area 44 to drain through conduit 50 into the drain conduit 60 thus allowing the fluid under pressure in the cylinder area 45 to overbalance the fluid pressure in the cylinder area 44 and move the piston 43 to the left in a manner to change the capacity control to a lower or closed position.

As shown by FIG. 5 of the drawing, when solenoid coil SB is energized valve VB will be operated to allow the fluid under pressure in the cylinder area 45 to drain through conduit 51 to the fluid pressure return conduit 60, thus allowing the pressure in the cylinder area 44 to overcome the pressure in the cylinder area 45 and move the piston to the right in a manner to change the capacity control to increase the capacity or open the intake valve as the case may be.

In accordance with the invention a sensing control system for supplying electric energizing signals selectively to the valve solenoid coils SA and SB is arranged to first apply an intermittent electrical signal to the requisite valve solenoid coil when the response of the refrigeration system first tends to deviate from a preset condition. As the deviation from the preset condition may increase further, the frequency and/or the duty cycle of the intermittent electrical signal to the respective solenoid valve solenoid coil SA or SB is increased until it will become a continuous electrical signal when the deviation exceeds a predetermined amount. For example, assuming it is desired to maintain a water temperature in the chiller outlet conduit 26 of about 45, the control of the invention may be within a given period of time that the associated valve solenoid will be energized to adjust the capacity control accordingly. The term duty cycle is a reference to the total actual time the intermittent signal occurs within a given period of time. Thus a higher frequency intermittent signal has a higher duty cycle or a given frequency of intermittent signal with longer on than off time has an increased duty cycle.

FIG. 6 of the drawings illustrates a simple electromechanical system for producing the required control signals but it should be understood that the invention is not to be limited to the particular electromechanical arrangement being described. A temperature sensing bellows 70 has its movable piston rod 71 adjustably connected through the adjustment device 72 to the movable platform 73 pivoted at 74 on a supporting base 75. A fixed contact supporting member 76 is secured to the fixed support 75 and its contact heads 77 and 78 may be respectively engaged by movable switch contacts 79 and 80 corresponding to the control contacts Ca and Ch shown by FIG. 1 of the drawings. The temperature sensing bulb 27 shown by FIG. 1 of the drawings is connected to the bellows 70 and when the refrigeration system condition being sensed, in this case the chilled water temperature, deviates from the preset condition, the bellows 70 will pivot the platform 73 to move contact 79 into engagement with contact 77 when the temperature of the chilled water first begins to rise above a desired preset condition. Alternately, if the temperature of the chilled water drops below the preset condition, the platform 73 will be moved in a direction to bring the contact 80 into engagement with the contact 78. Contacts 79 and 80 are supported on respective bimetallic strips 81 and 82 and a respective heater wire 83 and 84 is coiled around a respective bimetal strip 81 or 82. In accordance with the invention the arrangement is such that as soon as current flows through the respective bimetallic strip 81 or 82 upon closure of the associated contacts 79 or 80, an electric current will also pass through the heating coils 83 or 84 to heat the associated bimetallic strip in a manner to repeatedly make and break the contact. Thus, when the movable platform 73 is moved slightly to first bring a respective contact 79 or 80 into an engagement with the fixed contact 77 or 78, the contact closure will be of an intermittent nature as the associated bimetallic strip 81 and 82 alternately heats and cools. However, when the sensed condition has deviated beyond a predetermined amount say for example a maximum of 5 deviation, the movable platform 73 will have been moved sufliciently far to maintain a solid contact between the movable and fixed contact even though the associated bimetallic strip 81 or 82 may be continually heated by the associated heating coil 83 or 84. A simple means for adjusting the position of the respective movable contact 79 or 80 relative to the fixed contact 77 or 78 is shown to be the movable supporting block 85 or 86.

Referring now to FIG. 7 of the drawings, a simplified wiring diagram for the capacity control system will be described. A source of 24-volt control voltage is shown to be the transformer secondary winding 109, connected to the AC supply lines 101 and 102. Control signal voltage from line 101 is connected through normally closed contacts 103 of the overload relay OR to the movable arm 104 of a manual and automatic selector switch. When the movable selector switch arm 104 is moved to the dotted line position, control voltage through the normally closed contacts 103 may be supplied through either of the manual capacity control switches 105, 106 to the respective control valve solenoid coil SA or SB and to the line 102. When the manual switch 105 is moved to the closed position, the solenoid coil SA will be energized to move the capacity control in the increase capacity direction towards maximum capacity. On the other hand when the manual switch 106 is operated, the solenoid coil SB will be energized to move the capacity control in the decrease capacity direction towards the minimum capacity position.

When the selector switch 104 is in the solid line position shown, the energization of the respective valve solenoids SA and SB will be automatically controlled in response to the condition sensor 30. If the sensed condition begins to deviate in a manner to require increased capacity, CA contact 79 will engage the contact 77 in a manner to provide an intermittent electrical energizing signal to the solenoid coil SA. As previously described, should the sensed condition deviate further requiring a more rapid response of the capacity control to an increase capacity position, the frequency and/or the duration (i.e. duty cycle) of the intermittent signal by contacts 77 and 79 on line 107 to the valve solenoids SA will increase until it may actually become a continuous signal when the deviation exceeds the maximum preset deviation amount. Similarly, should the deviation of the sensed refrigeration condition be such as to require a decreased capacity of the centrifugal compressor, Cb contacts 78 and 80 would close in a manner to provide at first an intermittent signal on line 108 to the valve solenoid SB increasing in frequency and/or duration as the deviation may increase to a continuous signal when the deviation exceeds a predetermined deviation amount.

In order to prevent overloading of the centrifugal compressor and its electric motor 10, an overload relay OR responds to an excess of electric motor current to open normally closed contacts 103 and closed normally open contacts 109. This operation of the overload relay OR provides a continuous electric energizing signal to the valve solenoid SB thus moving the capacity control in the decreasing capacity position direction towards the minimum capacity position. It is obvious that the solenoid coil SB will remain energized so long as the overload relay OR is energized in response to excess current drawn by the electric motor 10. As soon as the current drawn by the electric motor drops below or to a predetermined point below the overload amount, the overload relay OR will deenergize to again reclose contacts 103 and open contacts 109 enabling the capacity control system to be operated either automatically or manually as previously described to obtain the desired refrigeration system condition.

Various modifications will occur to those skilled in the art.

I claim:

1. A refrigeration system comprising a centrifugal refrigerant compressor, a condenser, an expansion valve and an evaporator connected in a refrigeration circuit, said compressor having an axial suction gas inlet, movable compressor capacitor control means in said inlet, means forming a cylinder passage, means including a piston slidable in said passage for moving said control means towards increased or lower capacity positions, said passage having a first portion into which fluid under pressure is applied to move said piston in one direction to move said control means towards higher capacity positions, said passage having a second portion into which fluid under pressure is applied to move said piston in the opposite direction to move said control means towards lower capacity positions, a compressed fluid supply tube, a fluid return tube, a first two-way valve connected to said tubes and to said first passage portion, a second two-way valve connected to said tubes and to said second passage portion, said first valve in a first position routing fluid from said supply tube into said first passage portion, and in a second position routing fluid from said first passage portion into said return tube, said second valve in a first position routing fluid from said supply tube into said second passage portion, and in a second position routing fluid from said second passage portion into said return tube, means including a first solenoid coil for adjusting, when energized, said first valve to its said second position, and for adjusting when deenergized, said first valve to its first position, means including a second solenoid coil for adjusting, when energized, said second valve to its said second position, and for adjusting, when deenergized, said second valve to its first position, said coils being normally deenergized, control signal means responsive to variations of a capacity controlled sensed condition of the refrigeration system below and above a preset condition to provide respective electric energizing signals to said first and second solenoid coils respectively, said signal means including first means to cause the electric energizing signal therefrom to be varying from intermittent to a constant signal as the sensed condition decreases below the preset condition, and said signal means including second means to cause the electric energizing signal therefrom to be varying from intermittent to a constant signal as the sensed condition increases above the preset condition.

2. The invention of claim 1 in which said movable capacity control means is comprised of rotatable inlet spin vanes.

3. The invention of claim 1 in which said movable capacity control means is comprised of a rotatable throttle disk.

4. The invention of claim 1 in which said sensed condition is responsive to evaporator temperature.

5. The invention of claim 1 in which said compressor is powered by an electric motor and there is circuit means responsive to motor overload current for deenergizing said second solenoid coil and continuously energizing said first solenoid coil.

6. The invention of claim 4 in which said compressor is powered by an electric motor and there is circuit means responsive to motor overload current for deenergizing said second solenoid coil and continuously energizing said first solenoid coil.

7. The invention of claim 1 in which there is provided respective manually operated switch means for energizing said first and second solenoid coils respectively.

8. The invention of claim 1 in which said first and second means cause the respective energizing signals to vary in frequency increasing to a constant signal as the sensed condition deviates above or below the preset condition respectively.

9. The invention of claim 1 in which said first and second means cause the respective energizing signals to vary in duty cycle increasing to a constant signal as the sensed condition deviates above or below the preset condition respectively.

References Cited UNITED STATES PATENTS 2,983,111 5/1961 Miner 622l7 3,081,604 3/1963 Nzmishiak 622l7 3,204,423 9/ 1965 Resh 622l7 3,248,896 5/1966 Plaster 62-209 MEYER PERLIN, Primary Examiner US. Cl. X.R. 62203, 209, 217 

